This invention relates to light source apparatus and, more particularly, to a light source apparatus for endoscopic photographing systems for photographing a body cavity with such medical apparatus as endoscopes.
Generally, endoscopic photographing is effected when the body cavity is observed with an endoscope. Since the body cavity is dark, it is not necessary to effect the photographing on the basis of the operation of the camera shutter, that is, the operation of passing and blocking light from a light source can be made to be the shutter operation. Since a light source apparatus for endoscopic photographing is required to provide light of a great dose, a xenon lamp is used. However, repeatedly operating the xenon lamp at short intervals is undesirable from the standpoint of its service life. Accordingly, the light source apparatus for an endoscope generally uses a shutter plate, which is provided between the xenon lamp and a light guide for leading light from the xenon lamp to an objective section of the endoscope and serves to pass and block the light from the xenon lamp. The passing and blocking of light from the xenon lamp are controlled by controlling the shutter plate from a rotary solenoid or the like. When the solenoid is in the energized state, it acts to let the shutter plate pass the light from the xenon lamp without being blocked, while in the de-energized state it lets the shutter plate block the light. Usually, for endoscopic photographing an ordinary single-lens reflex camera body is mounted in front of the eyepiece of the endoscope. The photographing is started by depressing a shutter release button of the camera. The xenon lamp is held "on" during the presence of a synchronizing signal from the camera, and the solenoid is energized according to the synchronizing signal. Light reflected from the illuminated scene is received by a light-receiving element in the endoscope, and the output signal from the light-receiving element is integrated. The integral value thus obtained is compared in a comparator with a predetermined value. When the integral value exceeds the predetermined value, the solenoid is de-energized to let the shutter plate block light from the xenon lamp, thus bringing an end to the exposure of the photographic film. After the de-energization of the solenoid, the synchronizing signal is still present so that the xenon lamp remains "on". Therefore, after the de-energization of the solenoid the integral value is likely to be varied due to noise or the like, and sometimes it is possible that the comparator produces an erroneous output to erroneously energize the solenoid again. In such a case, proper exposure cannot be obtained.
An object of the invention is to provide a light source apparatus for endoscopic or like photographing system which can prevent erroneous operation of a shutter mechanism due to noise or other causes and resultant loss of proper exposure from occurring.